U.S. Pat. No. 6,528,587 of the Applicant Company discloses a composition comprising metallocene PE and non-metallocene LLDPE cografted with unsaturated carboxylic acid diluted in SBS. This document does not relate to multilayer structures comprising a PS layer. To date, coextrusion ties for structures comprising at least one PS layer are ethylene/vinyl acetate copolymers grafted with maleic anhydride.
It has now been found that, within a given range of amount of styrene in the SBS block copolymer, a coextrusion tie is obtained which makes it possible to efficiently tie PS layers to layers, for example, of PE, polyamide (PA) and saponified copolymers of ethylene and vinyl acetate (EVOH), whereas this is not the case outside this range.
This tie thus makes possible the preparation of various structures comprising, inter alia, a layer of polystyrene (PS) with good adhesion values, and has the advantage of exhibiting good heat resistance contributed by the styrene part of the composition. This is a noticeable advantage during the preparation of the structure or of an object produced using the structure with heat sealings or during pasteurization, for example. Another advantage of the ties of the present invention relates to their manufacture. These ties are prepared by melt blending and generally by melt grafting. The tie is recovered in the form of granules at the outlet of an extruder or of any other equivalent device. The Applicant Company has found that this granulation is much easier than for grafted ties of ethylene/vinyl acetate type.